Float glass is produced by continuously pouring out the glass melt on a tin bath, which is heated in an elongate tank, and the resulting glass ribbon.
Float glass is then finished by the longitudinal cutting and cross-cutting of the glass ribbon which emerges from the float glass production process at a defined feed rate. Here, the longitudinal cutting is carried out by longitudinal-cutting wheels which are installed in stationary fashion in an appropriate position above the glass ribbon, and the cross-cutting is carried out with the aid of cutting bridges and cross-cutting wheels which move thereon transversely above the glass ribbon.
Although it is technically conceivable to completely avoid particle inclusions or impurities in the glass when producing glass panes in the float glass process, this is scarcely possible using economically acceptable measures. This is why it is not surprising that the glass is accompanied by impurities, for example in flat glasses, and inclusions are present in the glass matrix. Among these inclusions, it is necessary to emphasize, in particular, nickel sulfide inclusions and inclusions of refractory materials, which generally make up the largest proportion of these impurities and can often be present with a size of up to about 600 micrometers.
Inclusions or particles of nickel sulfides or refractory materials in the submillimeter range are not perceived by the human eye and therefore do not influence the esthetic appearance of glass panes or similar products. However, inclusions such as these represent foreign bodies which have different material properties to glass and, under certain circumstances, for example after a hardening process, may therefore lead to spontaneous breaking of the glass. Such spontaneous breaking, as is observed, inter alia, in the case of facade claddings, may entail considerable personal injury and material damage. It is therefore necessary to try to use suitable methods to obtain information about possible inclusions, even before further use, in order to be able to separate out corresponding glass proportions in good time.
Optical investigation methods have already been proposed for the detection of inclusions in flat glass; these substantially involve the scattering of laser light in the amorphous glass and the analysis of the scattered light. Although this generally makes it possible to detect inclusions in a very reliable way, it is disadvantageous that this method always uses laser light and therefore results in a relatively large outlay on apparatus. In addition, the usable cross section of a laser beam is limited and, in view of the large glass surface areas to be investigated, this therefore calls for either a plurality of lasers to be used or for an increased amount of time as a result of the selective investigation of relatively small surface areas.
Therefore, the object of the method known from WO 2007/051582 A1 is to detect particles in a glass object in a simple manner and without an external light source.
The method described in said document substantially involves electromagnetic radiation which is emitted from the glass object during the solidification of the liquid glass at ambient temperature being recorded in a locally resolving manner, and the location-dependent detection of the radiation which is determined in this way being evaluated in order to determine inclusions (cf. claim 1).
For this purpose, the glass object is moved uniformly and the emitted radiation is recorded using one or more line detectors or area detectors, such as a CCD camera or a CMOS camera. Here, the exposure time of an area detector is adapted to the speed at which the object moves (cf. claim 4).
The inclusions which are discovered then have to be identified and cut out. For reasons which are apparent, this process should produce the least possible waste and take place quickly, without disrupting the ongoing production process.
In the production of auto glass, which is known from DE 10 2004 025 329 A1, for example, a considerable amount of waste is accrued if the trapezoidal vehicle windscreens are cut out from the prepared rectangular blanks.
In order to reduce the waste, the cutting pattern should substantially be selected in such a way that in each case two glass plates which are oriented so as to be rotated by 180° in relation to one another and have a corresponding inclined edge are arranged in the form of a strip transversely above the float glass ribbon such that they butt directly against each other and are aligned with one another with their parallel trapezium edges, and successive strips of pairs of glass plates directly adjoin each other in the direction of the float glass ribbon. In this case, the inclined trapezium edges should be cut by means of longitudinal-cutting elements and the parallel trapezium edges should be cut by means of cross-cutting elements (cf. in this respect claim 1).
DE 10 2004 025 329 A1 does not disclose how the glass proportions, which are cut away by the cutting elements and represent waste, are severed from the useful areas.
EP 1 475 356 B1 discloses a method for separating glass panels into glass blanks according to a predefined division pattern, in which method glass panels are separated into glass panel blanks in at least one first separation step in one direction (X cuts), and these glass panel blanks are then separated into glass blanks in at least one second separation step in a direction perpendicular to the first separation step (Y cuts).
This document intends to claim that the glass panel blanks which are obtained after the separation in the X direction on the table provided downstream of the first separation site (A) are jointly supplied to a second separation site (B), at which the glass panel blanks are separated along the Y cuts.
This document does not refer to the actual cutting-to-size and severing process.
In addition, there are devices for severing a glass ribbon which have rollers which can each be moved from their position in the roller table.
These are known from U.S. Pat. No. 1,861,665 A, cf. claim 1 and FIG. 4, from BE 392 056 A, cf. FIGS. 10 to 12 and claims 7 to 9, and from FR 2 530 612 A1, cf. FIG. 1 and claims 7 and 8.